1. Field of the Invention
The present invention relates to an image recording apparatus which records an image by moving a recording position of image data to be recorded on a recording medium as an image corresponding to a positional deviation of a conveyed recording medium (for example, recording paper), and an image recording method of the image recording apparatus.
2. Description of the Related Art
In a recording head of each color provided on a general consumer color ink jet printer, a nozzle column composed of plural nozzles for ejecting ink in a direction which conforms to a conveying direction (or called Y direction) of a recording medium is formed and mounted on a carriage. Hereinafter, a direction perpendicular to the conveying direction of the recording medium is called width direction of the recording medium (or called X direction). If ink of each color is ejected to the recording medium while the carriage is reciprocated for scanning in the width direction of the recording medium, a color image or the like is recorded on the recording medium. This type of the color ink jet printer is called serial type.
An available printer of different type from the serial type includes an ink jet printer having the same number of recording heads as that of prepared colors, in which a nozzle column having the width of the recording medium or longer is equipped along the X direction. In this ink jet printer, each recording head is disposed and fixed above a conveyed recording medium, and when the recording medium passes below the nozzle column of the recording heads, ink of each color is ejected from each recording head so as to record a color image or the like. Such a color ink jet printer is called full line type.
This full line type ink jet printer includes one disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2002-120386. According to the ink jet printer, plural recording heads whose nozzle column is relatively short are disposed in a staggered manner so as to be departed back and forth in the Y direction at a predetermined distance, while extended over a length not shorter than the width of the recording medium along the X direction. Further, as for this disposition, the nozzle columns in short-length recording heads adjoining each other in the Y direction partially overlap. With the overlapping, no gap (portion at which no ink is ejected) occurs in, for example, a 1-line image formed by each recording head. As an example of the disposition of such recording heads, as shown in, for example, FIG. 17, three short-length recording heads disposed with a predetermined distance in the X direction (including K1 recording head) and three short-length recording heads disposed with a predetermined distance in the X direction (including K2 recording head) are arranged in two columns with a predetermined separation distance (nozzle column deviation amount) in the Y direction.
In image data developed on the short-length recording head having such a configuration, plural 1-line image data recorded in the X direction are developed in plural quantities in the Y direction without any gap (two-dimensional development). On the other hand, an image data memory is used for processing of image data composed of plural 1-line image data (data write or read out of written data), so that image data to be processed is stored so as to be developed to a row and a column in a two-dimensional map.
The image data is stored such that the one-line data items are recorded in the same row, each one-line item in the column direction, depending on the storage capacity of the image data memory.
In the above-described ink jet printer having the short-length recording heads loaded thereon, an image of the 1-line image data must be recorded by driving the three short-length recording heads (including K1 recording head) at an ink ejection timing α1 and driving the other three short-length recording heads (including K2 recording head) at an ink ejection timing α2.
The recording medium can be conveyed in a shift laterally (X direction) as shown in FIG. 18 because of a conveyance error or the like of the conveying mechanism. In the ink jet printer, its image recording position needs to be controlled by moving corresponding to the lateral deviation amount of the recording medium.
If the image is recorded on a recording medium deviated laterally, even a nozzle in the short-length recording head not opposing any recording medium due to the lateral deviation ejects ink. A conveying member such as a conveying belt of the conveying mechanism is stained by this ink. The stain of the conveying member adheres to a non-image recording face (face on which no image is recorded at the time of single-face image recording) of the recording medium, thereby causing contamination.
The 1-line image data is formed with plural short-length recording heads in the ink jet printer shown in FIG. 18. Therefore, the control method is different from the control in image recording of an ordinary ink jet printer whose nozzle column is not shorter than the width of the recording medium. That is, since, according to the image recording control of the ink jet printer, the nozzle columns of the short-length recording heads are disposed in a shift in the Y direction, image recordings at different ink ejection timings α1 and α2 are necessary.
On the other hand, since the three short-length recording heads (including K1 recording heads) and the three short-length recording heads (including K2 recording head) are disposed in a shift back and forth in the Y direction, the 1-line image data needs to be distributed to image data to be recorded at the ink ejection timing α1 and image data to be recorded at the ink ejection timing α2 at a joint of respective nozzle columns of adjoining recording heads.
Therefore, the 1-line image data in FIG. 18 is comprised of image data for the three short-length recording head including the K1 recording head and image data for the three short-length recording head including the K2 recording head.
In the case where the image recording is carried out by using the short-length recording heads disposed such that the end portions of the respective nozzle columns overlap each other in the Y direction as shown in FIG. 18, it is necessary to execute image-recording density-varying processing for making a joint in a recorded image at a portion in which nozzle columns of the adjoining recording heads join less conceivable.
The term “image-recording density” means the optical density of the image formed on the recording medium by applying ink droplets from the recording nozzles onto the recording medium.
If the density-varying processing is not carried out, the joint portion receives ink ejection in duplicate from two short-length recording heads while the other portion than the joint portion receives ink ejection from a single short-length recording head, and therefore, there is a fear that a stripe-like difference in density may be found in the recorded image.
As described above, the image recording apparatus carries out the full line image recording by using plural short-length recording heads disposed so as to form an image as if their nozzle columns are connected in line in the width direction of the recording medium. The image recording apparatus requires X-direction recording position moving processing to meet a deviation of the conveying position of the recording medium, image data distribution processing for distributing image data with a joint of the full line image as a boundary, and density-varying processing for making a joint of a partial image recorded by the short-length recording head less conceivable.